Spotify has launched a beta version of their web based radio player. And it already works on the Playbook. When the Blackberry 10 devices launch, it will work on those too.
For the people who are testing it ( a small select group), Spotify has no issues working on the Playbook browser. Unfortunately, it is not an open beta.
What Spotify had to say:
“Potentially it’s a great additional feature for times you can’t play music through the desktop app, like at work or at a friend’s house. We’ll have more detail on the web player next year,” Spotify said.